Numerous attempts have been made to overcome the problems of shading but so far these have met with only limited success. Indeed shading is one of the reasons why velvet pile carpets are less popular with both customers and manufacturers and the existence of problems with shading has led carpet manufacturers to offer different types of carpet such as those including a sculptured pile or a twist pile which either do not suffer from this problem or only suffer from it to a much smaller extent.
We believe the effect of shading is caused by the carpet pile tufts in some areas of the carpet being oriented at a slightly different angle with regard to the backing of the carpet from those in other areas. However, attempts to measure such angles and compare the angles in different regions where shading appears have not shown any measurable difference in their angle of orientation. Most carpet pile tufts are not placed perfectly normal to the backing and usually there is some "lay" of the pile tufts. In woven carpets this lay is caused by the tuft insertion technique and the beat-up operation. The pile tufts lay in the direction towards the already woven length of carpet and, usually to one side or the other when viewed from the already woven length of carpet.
GB-A-2,067,614 discloses a system for arranging long fibres of a material in a generally uniform direction before a treatment stage, for example dyeing, to ensure the subsequent treatment is uniformly applied to all fibres. subsequent treatment is uniformly applied to all fibres. This orientation of the fibres is achieved by brushing or combing the fibres, for example by a brush roller having fine wire bristles or using an air brush. The present inventors have found that brushing or combing the pile tufts of a carpet in this way cannot achieve uniform orientation of the tufts and does not overcome shading of the carpet.